This invention relates to a metallized polypropylene film containing a metal adhesion layer comprising a polymer wax and a polyolefin resin. In particular, a polyethylene wax is blended with a polypropylene resin.
Biaxially oriented polypropylene metallized films are used for many packaging applications, particularly in food packaging, because they have important sealing and protective qualities. The films minimize the amount of light, moisture, and oxygen which can normally enter an ordinary, unprotected package. The films are often used in food packaging in combination with gas-flushing applications to protect the contents from moisture and oxidation. Also, the films often provide a heat sealable inner layer for bag forming and sealing.
Metallized films used in vertical-form-fill-seal (VFFS) packaging provides an excellent barrier in both unlaminated or laminated forms. However, because of the wide variety of forming collars used, bag sizes, filling speeds, and machine tensions used during the process of bag-forming, the laminated packaging containing the metallized film can be stretched in the packaging machine from 5 to 10% beyond the dimensions of the original film packaging. This stretching may cause fracture or cracks to form in the metal layer of the film. As a result, the packaging loses its protective properties. For instance, oxygen can readily pass through a damaged packaging film and cause unwanted oxidation of the contents.
U.S. Pat. No. 5,698,317, which is incorporated herein by reference, discloses the use of a four layer packaging film having a polyolefin resin layer sandwiched between a polyolefin resin layer comprising a petroleum or terpene resin and a heat sealable layer or non-sealable winding layer. A metal layer is then deposited on the surface of the polyolefin resin layer. The metal layer is deposited following the discharge treatment of the polyolefin resin layer.
The present invention improves upon the moisture and gas barrier properties as well as the durability of the metal layer.
The invention helps solve the problem of leaky bags associated with conventional metallized film packaging and the bag-forming process by providing an improved polyolefin resin layer. The improved resin layer comprises a polymer resin with a polymer additive to form a resin layer. The addition of the polymer additive to the polymer resin enhances the adhesion between the blended polymer resin layer and the metal layer, and thus improves upon the durability of the packaging film during the bag forming process. The invention provides a metallized, laminate film which exhibits little or no fracture or cracking during the bag-forming process. The enhanced adhesive properties of the invention also improves upon the moisture and gas barrier properties of laminate film.
One embodiment of this invention is a laminate film comprising a polymer core layer; a resin layer disposed on a surface of said polymer layer; and a metal layer deposited on a surface of said resin layer; wherein the laminate film has metal adhesion of 2 or more; and wherein the laminate film has O2TR of 100 cc/m2/day or less at 38xc2x0 C. and 0% relative humidity as measured on a 15 xcexcm laminate film elongated 9% in the machine direction.
Another embodiment is a laminate film comprising a polymer core layer; a resin layer disposed on a surface of said polymer layer; a metal layer deposited on a surface of said resin layer; and means for enhancing adhesion between the resin layer and the metal layer. The means for enhancing adhesion could be an additive, which is polymeric or non-polymeric, organic or inorganic.
Another embodiment of this invention is a method of manufacturing a laminate film, comprising extruding a polymer core layer; extruding a resin layer disposed on a surface of said polymer layer; and depositing a metal layer on a surface of said resin layer; the laminate film having metal adhesion of 2 or more; and the laminate film having O2TR of 100 cc/m2/day or less at 38xc2x0 C. and 0% relative humidity as measured on a 15 xcexcm laminate film elongated 9% in the machine direction.
One embodiment of this invention is a method for food packaging, comprising obtaining a laminate film and covering food with the laminate film; the laminate film comprising a polymer core layer; a resin layer disposed on a surface of said polymer layer; and a metal layer deposited on a surface of said resin layer; wherein the laminate film has metal adhesion of 2 or more; and wherein the laminate film has O2TR of 100 cc/m2/day or less at 38xc2x0 C. and 0% relative humidity as measured on a 15 xcexcm laminate film elongated 9% in the machine direction.
The invention is of a laminate film comprising: a polyolefin resin layer; a polymer core layer; a heat sealable layer or non-sealable winding layer formed on the surface of a polymer core layer opposite the polyolefin resin layer; and a metal layer disposed on the polyolefin resin layer. The polymer core layer is sandwiched between the resin layer and the heat sealable layer. The invention contains a polyolefin resin layer having about 1 to 30 percent by weight, preferably 1 to 20 percent by weight, more preferably 1 to 10 percent by weight of a polymer additive. The polymer additive is selected from a group of synthetic polymer waxes. In the preferred embodiment a polyethylene crystalline wax is added to a polypropylene resin. The polyolefin resin layer may optionally contain up to 1000 ppm of antiblock additives such as silicas, aluminosilicates, or metal-aluminosilicates. The heat sealable layer or non-sealable winding layer may also contain antiblock components such as silicas, aluminosilicates, or polymeric antiblocks such as crosslinked silicone polymer in the amount of 0.10-0.50% by weight of the heat sealable or non-sealable winding layer. It is also preferred that the surface of the polyolefin resin layer be corona discharged treated to give excellent printability and promote adhesion between the resin layer and the metal layer. The metal layer is preferably a vapor deposited metal, preferably vapor deposited aluminum.